The long-range interest underlying this proposal is the area of cellular interaction: how cells recognize and communicate with one another. The proposed project is the continued development of a tissue culture system for the investigation of neurospecificity. It will combine my background in biochemistry (1-3) with the electrophysiological expertise of E. J. Furshpan and D. D. Potter. The first phase of this project has centered on establishment of techniques and conditions for isolation and growth of sympathetic neurons in culture. The plans for future biochemical work on the cultures can be grouped as five interrelated categories. (a) Catecholamine pools. The immediate plans for the biochemical studies involve further analysis of the number, size, turnover rates and subcellular distribution of the catecholamine pools discussed in Section A2. "Trophic" effects. Also planned for the coming year is an investigation of the possible effects of the presence of other cell types (target cells, non-target cells, and satellite or glial cells) on the sympathetic neurons. These studies will be concerned with the effects of other cell types on the survival of the neurons, or their ability to synthesize and accumulate catecholamines and protein, and on the timing and magnitude of the developmental changes outlined in Section A2. (c) Neuronal Proteins and Lipids. In addition, we propose a more detailed investigation of the neuronal protein and lipid compositions, with special reference to those macromolecules synthesized just before or at the time of synapse formation. (d) Hormonal effects. Two other projects proposed are of a long-term nature and depend in part on successful completion of the studies now in progress and of those planned for next year. The first would consider endocrine effects on the development and catecholamine synthesis of the neurons, taking advantage of the possibility for controlling the chemical and cellular environment of the neurons in culture. (e) Molecular determinants of Neurospecificity. The second long-range project will be an effort to identify the membrane components which play an important part in determining whether or not a neuron "recognizes" a target cell and forms a synapse.